In modern intensive medicine a successful therapeutic intervention is only possible on the basis of extensive diagnostic information. Knowledge of cardiac and respiratory activity as physiological functional parameters is essential. They are usually monitored using a plurality of measuring elements such as cardiac catheters, special breathing sensors, etc. For this monitoring, not only is the display and evaluation of the functional parameters difficult to coordinate, but also the placement of the detection instruments within the heart and lungs of a patient is difficult.
Many such functional parameters are also dependent upon a patient's exercise, so that they can also be used to control dynamic variations in the pacing rate of a cardiac pacemaker.
Some available publications describe pacing rate control of a pacemaker by measured signals based on the detection of one physiological functional parameter. Thus, in U.S. Pat. No. 4,566,456, G. Koning et al., Jan. 28, 1986, the systolic pressure and change in time of the right ventricular pressure is used as the functional parameter. In German Offenlegungsschrift No. 27 17 659, A Wirtzfeld, et al., published Oct. 26, 1978, the central venous oxygen saturation parameter is used. In U.S. Pat. No. 4,535,774, W. H. Olson, Aug. 20, 1985 and U.S. Pat. No. 4,674,518, R. W. Salo, June 23, 1987, the ventricular stroke volume of the heart is determined by means of an impedance measurement. In U.S. Pat. No. 4,567,892, G. Plicchi, et al., Feb. 4, 1986, the respiratory rate is determined from an implanted secondary electrode by an impedance measurement. In U.S. Pat. No. 4,697,591, A. Lekholm, et al., Oct. 6, 1987, the respiratory rate is determined from impedance across the chest cavity by using the can and heart implant electrodes. In U.S. Pat. No. 4,596,251, G. Plicchi, et al., June 24, 1986, the respiratory minute volume is measured by impedance changes from at least one electrode located in the chest cavity. Other related respiratory rate controls are effected in U.S. Pat. Nos.: 3,593,718, J. L. Krasner et al., July 20, 1971; 4,721,110, M. S. Lampadius, Jan. 26, 1988 and 4,702,253, T. A. Nappholz et al., Oct. 27, 1987. In U.S. Pat. No. 4,291,699, L. A. Geddes, et al. Sept. 29, 1981 the change of impedance between two electrodes in one ventricle is used to indicate and control fibrillation of the heart. In U.S. Pat. No. 4,576,183 G. Plicchi, et al., Mar. 18, 1986 subcutaneous electrodes in a patient's chest are used to measure impedance for obtaining a respiratory parameter.
Recently there have also been proposals to control the pacing rate of a cardiac pacemaker from two or more physiological functional parameters. In German Patent No. P 36 31 155.C2, published Mar. 24, 1988, pacing rate is controlled for stable long-term control from the temperature of the venous blood within the heart and from an activity sensor for short-term exercise related activity. The temperature signals can be modulated by the activity signals for an optimal adaptation of the pacing rate to the particular exercise of the patient. Different sensors may be used to check the two functional parameters. The pacemaker control is based on the finding that essentially only absolute parameters such as the blood temperature and activity should be used as absolute values for determining a relationship between these parameters and the pacing rate, whereas other physiological functional parameters are merely relative parameters, which at least impede stable long-term control of the pacemaker.
U.S. Pat. No. 4,722,342, D. Amundson, Feb. 2, 1988 provides a plurality of different body activity sensors to derive variable pacer controls for body activity.